Regular electric and electronic apparatus are commonly operated through a keyboard or key pad device. The keyboard or key pad device on a mobile telephone, notebook computer, etc., is compact, and therefore the keys are arranged close to one another. For the aged, it is difficult to distinguish the patterns or numerals on the keyboard or key pad of a small electric or electronic apparatus.
Furthermore, FIG. 6, labeled "prior art", shows a key switch D for a key pad device according to the prior art, comprised of a unitary plastic key body and a conductive rubber pad fastened to the plastic key body for triggering the circuit board below.
Because the melting point of the plastic key body is about 120.degree. C. and the rubber is either vulcanized and therefore non-fusible or, if thermoplastic, has a melting point of about 170.degree. to 180.degree. C., the rubber cannot be sealed to the plastic key body through any conventional heat sealing process. Therefore, a bonding agent is commonly used to fasten the rubber to the plastic key body. Because the rubber is fastened to the plastic key body by a bonding agent, the rubber may disconnect from the plastic key body after long uses.